阅读说明：本技术 一种耐水性生物淀粉塑料及制备方法 (Water-resistant biological starch plastic and preparation method thereof ) 是由 陈庆 曾军堂 白涛 司文彬 于 2020-07-21 设计创作，主要内容包括：本发明涉及可降解塑料技术领域,特别是涉及一种耐水性生物淀粉塑料的制备方法,包括：将淀粉加入混合机中,真空脱除淀粉的结晶水；将无水淀粉研磨细化至纳米级,得到纳米无水淀粉；将硬脂酸、石蜡、聚乙烯蜡熔融混合得到油状混合物,再将纳米无水淀粉加入油状混合物中,高压均质后得到均质浆料；将均质浆料静置冷凝后粉碎,即得耐水热塑性淀粉；将耐水热塑性淀粉、聚乙烯、相容剂混合,再送入挤出机挤出,即得。本发明解决现有技术中小分子增塑剂在高温加工增塑剂容易挥发且增塑剂残留在塑料制品中容易吸水析出的问题。上述制备方法预先将淀粉进行改性使制得的耐水性生物淀粉塑料具有良好的耐水性、耐热性以及性能均匀的优点。(The invention relates to the technical field of degradable plastics, in particular to a preparation method of water-resistant biological starch plastic, which comprises the following steps: adding starch into a mixer, and removing crystal water of the starch in vacuum; grinding and refining the anhydrous starch to a nanometer level to obtain nanometer anhydrous starch; melting and mixing stearic acid, paraffin wax and polyethylene wax to obtain an oily mixture, adding nano anhydrous starch into the oily mixture, and homogenizing under high pressure to obtain homogeneous slurry; standing and condensing the homogeneous slurry, and then crushing to obtain the water-resistant thermoplastic starch; mixing the water-resistant thermoplastic starch, polyethylene and the compatilizer, and then sending the mixture into an extruder for extrusion to obtain the water-resistant thermoplastic starch-polyethylene composite material. The invention solves the problems that the small molecular plasticizer is easy to volatilize during high-temperature processing and the plasticizer is easy to absorb water and separate out when remaining in plastic products in the prior art. The preparation method modifies the starch in advance, so that the prepared water-resistant biological starch plastic has the advantages of good water resistance, heat resistance and uniform performance.)

1. The preparation method of the water-resistant biological starch plastic is characterized by comprising the following steps:

step one, adding starch into a mixer, and removing crystal water of the starch in vacuum at 90-120 ℃ to obtain anhydrous starch;

step two, grinding and refining the anhydrous starch in the step one to a nanometer level to obtain nanometer anhydrous starch;

step three, melting and mixing stearic acid, paraffin and polyethylene wax at 80-90 ℃ to obtain an oily mixture, adding the nano anhydrous starch obtained in the step two into the oily mixture, and homogenizing under high pressure to obtain homogeneous slurry; wherein, the stearic acid, the paraffin, the polyethylene wax and the nano anhydrous starch are (5-8), (3-5) and (50-60) in sequence by weight;

step four, standing and condensing the homogenized slurry obtained in the step three, and then crushing to obtain the waterproof thermoplastic starch;

and step five, mixing the water-resistant thermoplastic starch, the polyethylene and the compatilizer in the step four according to the mass parts of (50-60), (30-40) and (3-5), then sending the mixture into an extruder for extrusion, and carrying out air cooling die surface grain cutting to obtain the water-resistant biological starch plastic.

2. The method for preparing the water-resistant biological starch plastic according to claim 1, wherein the method comprises the following steps: the temperature of vacuum removal in the first step is 100-110 ℃, the stirring speed is 50-150 r/min, the stirring time is 45-60 min, and the vacuum pressure is-0.06 MPa to-0.08 MPa.

3. The method for preparing a water-resistant biological starch plastic according to claim 1 or 2, wherein the method comprises the following steps: in the first step, the starch is at least one of corn starch, cassava starch and pea starch.

4. The method for preparing the water-resistant biological starch plastic according to claim 1, wherein the method comprises the following steps: grinding in the second step adopts a cyclone type air flow grinder, a ball mill, a circulating pipe type grinder or a flat type air flow grinder; the grain size of the nano anhydrous starch is less than or equal to 100 nm.

5. The method for preparing the water-resistant biological starch plastic according to claim 1, wherein the method comprises the following steps: in the third step, the stearic acid, the paraffin, the polyethylene wax and the nano anhydrous starch are sequentially (6-7), (4-5) and (54-58) in parts by weight.

6. The method for preparing the water-resistant biological starch plastic according to claim 1, wherein the method comprises the following steps: and in the third step, a plunger pump high-pressure homogenizer is adopted for high-pressure homogenization, the homogenization temperature of the plunger pump high-pressure homogenizer is 90-95 ℃, and the flow speed of the slurry in the plunger pump high-pressure homogenizer is 100-200 m/s.

7. The method for preparing the water-resistant biological starch plastic according to claim 1, wherein the method comprises the following steps: in the fifth step, the compatilizer is at least one of maleic anhydride grafted polyethylene, maleic anhydride grafted EVA and maleic anhydride grafted EAA; and the extruder in the fifth step is a co-rotating double-screw extruder with the length-diameter ratio of 35-40.

8. The method for preparing the water-resistant biological starch plastic according to claim 7, wherein the method comprises the following steps: the temperature of a first zone of the co-rotating double-screw extruder is 130-140 ℃, the temperature of a second zone of the co-rotating double-screw extruder is 140-150 ℃, the temperature of a third zone of the co-rotating double-screw extruder is 160-165 ℃, the temperature of a fourth zone of the co-rotating double-screw extruder is 170-175 ℃, the temperature of a fifth zone of the co-rotating double-screw extruder is 140-150 ℃, and the temperature of.

9. The method for preparing the water-resistant biological starch plastic according to claim 7, wherein the method comprises the following steps: the rotating speed of a main machine of the co-rotating double-screw extruder is 220-250 rpm, and the main feeding rotating speed is 20-30 r/min.

10. A water-resistant biological starch plastic is characterized in that: the water-resistant biological starch plastic is prepared by the preparation method of any one of claims 1 to 9.

Technical Field

The invention relates to the technical field of degradable plastics, in particular to a water-resistant biological starch plastic and a preparation method thereof.

Background

The biodegradable plastic is an energy-saving and environment-friendly new material. Because of containing active groups such as hydroxyl, ester, carboxyl and the like which are easy to be decomposed by microorganisms, when the biological filter is placed in a natural environment under certain temperature and humidity conditions, the biological filter is easy to be decomposed into water and carbon dioxide under the action of the microorganisms, thereby returning to the nature. Its development began in the last 70 th century. Through the development of more than 40 years, a solid technical foundation is reserved, the technology is continuously updated, and the product performance is continuously improved. With the continuous rise of market demand, the industrial transformation and application of various technical achievements become the key point of the development of biodegradable plastics.

In recent years, the country has vigorously promoted environmental protection products, encouraged the utilization of renewable biomass energy and the popularization and application of degradable plastics, and the production, sale and use of disposable non-degradable plastic products are prohibited. Therefore, there is a great market space for alternatives to biodegradable plastics. Among many biomass plastics, starch plastic is used as the plastic raw material with the lowest cost in the current bioplastic, and is used in huge amount in various packaging plastic products. The existing starch plastic has the capacity of large-scale production and use initially, the preparation process is relatively stable, and the raw material source is stable.

Starch is biodegradable, is one of important materials in biodegradable plastics, and is mature to be applied to preparing starch plastics at present. However, because the molecular chain contains a large amount of hydroxyl groups and strong hydrogen bonding exists between the molecular chains, the material has no thermoplasticity, is difficult to form and process and poor in water resistance, can not be used alone as a material generally, and generally needs to be made into a plastic alloy with other plastics. However, the strong polarity of the starch causes poor compatibility of the starch and the base resin, the adding proportion of the starch in the resin is limited, and the thermoplastic treatment is required to solve the problem of the limitation of starch processing. In this modern day era, where environmental protection is advocated, thermoplastic processing of starch has become an important research topic.

The Chinese invention patent CN201810969738.7 provides a preparation method of polyethylene starch plastic, firstly, ZrOCl.HO and concentrated phosphoric acid are utilized to prepare alpha-phosphoric acid pickaxe nano particles; then, carrying out hydrophobic modification on starch by a silanization reagent, and carrying out micronization treatment on the modified starch by a ball milling method to obtain nano-scale modified starch micropowder; and finally, putting the polyethylene, the nanoscale modified starch micropowder, the talcum powder, the calcium carbonate, the alpha-phosphoric acid pickaxe and the natural plasticizer into a high-speed mixer, uniformly mixing, plasticizing and extruding by a double-screw extruder, and cooling and granulating to obtain the polyethylene starch plastic. The polyethylene starch plastic prepared by the invention patent has strong water resistance and excellent mechanical property, starch is not easy to be gelatinized in the preparation process, and the obtained plastic is safe, nontoxic and completely degradable. The natural plasticizer in the polyethylene starch plastic is one of glycerol, glycol, sorbitol and polyethylene glycol 200, and the micromolecule plasticizer is hydrophilic and is difficult to bear higher processing temperature.

The Chinese invention patent CN201911371545.2 provides a bio-based polyethylene/starch blending modified blown film material and a preparation method thereof, and the bio-based polyethylene/starch blending modified blown film material comprises the following components in parts by weight: 25-45 parts of bio-based low-density polyethylene, 5-25 parts of bio-based high-density polyethylene, 4-20 parts of ethylene ethyl acrylate, 1-8 parts of compatilizer, 30-65 parts of starch, 3-19.5 parts of plasticizer, 1-8 parts of dispersant and 1-8 parts of accelerator. The film blowing material provided by the invention has the advantages of high biobased content, low melt index, good processability and strong mechanical property, and is beneficial to industrial popularization and utilization. The plasticizer of the bio-based polyethylene/starch blending modified blown film material is any two of white oil, deionized water and acetyl tri-n-butyl citrate. Because the micromolecule plasticizer is hydrophilic and is difficult to bear higher processing temperature, the micromolecule plasticizer (such as water and the like) of the bio-based polyethylene/starch blending modified blown film material volatilizes during thermoplastic processing, so that the starch shaping is lost, and the plasticizer is remained in a plastic product and is easy to separate out and absorb water.

The current thermoplastic processing of starch is mainly focused on plasticization with small molecule plasticizers: when the starch plastic is prepared, a large amount of small molecular plasticizers (such as glycerol, glycol, water and the like) are added to plasticize the starch, and the purpose of plasticization is to break hydrogen bonds of the starch and enable the starch to have thermoplasticity. However, the small molecular plasticizer is hydrophilic and is difficult to withstand higher processing temperature, starch shaping is lost due to volatilization of the small molecular plasticizer (such as glycerol, ethylene glycol, water and the like) during thermoplastic processing, and the plasticizer remains in a plastic product and is easy to precipitate and absorb water, so that the performance of the plastic product is poor. Although the starch is treated by using hydrophobic auxiliary agents such as white oil, stearic acid and the like at a later stage, the negative effects of the small-molecular plasticizer on the plasticizing of the starch are difficult to completely eliminate.

Disclosure of Invention

In view of the disadvantages of the prior art, the invention aims to provide a preparation method of a water-resistant biological starch plastic, which is used for solving the problems that small molecular plasticizers are easy to volatilize in high-temperature processing and the plasticizers are easy to absorb water and separate out when remaining in plastic products in the prior art, and also provides a water-resistant biological starch plastic. The preparation method modifies the starch in advance to ensure that the modified starch is resistant to water and heat and has certain thermoplasticity, and then the modified starch is mixed with polyethylene for extrusion to prepare the water-resistant biological starch plastic which has the advantages of good water resistance, heat resistance and uniform performance.

In order to attain the above and other related objects,

in a first aspect of the invention, a preparation method of water-resistant biological starch plastic is provided, which comprises the following steps:

step one, adding starch into a mixer, and removing crystal water of the starch in vacuum at 90-120 ℃ to obtain anhydrous starch;

step two, grinding and refining the anhydrous starch in the step one to a nanometer level to obtain nanometer anhydrous starch;

step three, melting and mixing stearic acid, paraffin and polyethylene wax at 80-90 ℃ to obtain an oily mixture, adding the nano anhydrous starch obtained in the step two into the oily mixture, and homogenizing under high pressure to obtain homogeneous slurry; wherein, the stearic acid, the paraffin, the polyethylene wax and the nano anhydrous starch are (5-8), (3-5) and (50-60) in sequence by weight;

Step four, standing and condensing the homogenized slurry obtained in the step three, and then crushing to obtain the waterproof thermoplastic starch;

and step five, mixing the water-resistant thermoplastic starch, the polyethylene and the compatilizer in the step four according to the mass parts of (50-60), (30-40) and (3-5), then sending the mixture into an extruder for extrusion, and carrying out air cooling die surface grain cutting to obtain the water-resistant biological starch plastic.

The preparation method modifies the starch in advance to ensure that the modified starch is resistant to water and heat and has certain thermoplasticity, and then the modified starch is mixed with polyethylene for extrusion to prepare the water-resistant biological starch plastic which has the advantages of good water resistance, heat resistance and uniform performance. The preparation method has the advantages that the whole process is simple, so that the difficulty of the processing technology is reduced, the raw material source is wide, the cost of the processing technology is reduced, the yield is high, and the utilization rate of the material is improved.

Completely removing crystal water in the starch by drying, and grinding and refining the starch to obtain the nano anhydrous starch. Most of the crystalline structure of starch disappears due to nanocrystallization, at which point the starch has theoretical thermoplasticity, but it is still difficult to directly thermoplastically process. And then adding the nano anhydrous starch into an oily mixture (formed by mixing excessive stearic acid, paraffin and polyethylene wax), and dispersing by using a homogenizer to completely disperse the nano anhydrous starch in the composition of the stearic acid, the paraffin and the polyethylene wax to obtain the waterproof thermoplastic starch. Stearic acid is used as a plasticizer to modify the starch, so that the modified starch has good plasticity. The polyethylene wax has excellent cold resistance, heat resistance, chemical resistance and wear resistance, and can be used as a lubricant, and the polyethylene wax has stable chemical property and good electrical property. The polyethylene wax is used as a lubricant to ensure that the starch is uniformly dispersed in the oily mixture, so that the dispersibility of the starch is improved, and the agglomeration phenomenon is avoided. The paraffin has certain water resistance, and can also be used as a plasticizer and a dispersant.

And mixing the water-resistant thermoplastic starch, polyethylene and the compatilizer, and performing screw extrusion granulation to obtain the water-resistant biological starch plastic. The water resistance of the water-resistant biological starch plastic is improved by breaking the crystalline structure of the starch through nanocrystallization and uniformly dispersing the nano starch by using excessive water-resistant lubricating materials because the water-resistant thermoplastic starch is not plasticized by using a small-molecule plasticizer.

Further, the temperature of vacuum removal in the first step is 100-110 ℃, the stirring speed is 50-150 r/min, the stirring time is 45-60 min, and the vacuum pressure is-0.06 MPa-0.08 MPa. The crystal water in the starch is removed in vacuum, on one hand, the vacuum removal can remove all the crystal water, and on the other hand, the vacuum removal can not introduce impurities (the impurities are prevented from influencing the performance of the nano starch). Stirring at a low speed in the removing process is used for accelerating the removing and removing all the crystal water of the starch, and on the other hand, the problem that the crystal water in the starch cannot be completely removed due to too high stirring speed is avoided.

Further, in the first step, the starch is at least one of corn starch, tapioca starch and pea starch. The starch can be selected from all conventional starches, but corn starch, tapioca starch and pea starch have wide sources and low cost, so that the corn starch, the tapioca starch and the pea starch can be selected as the preferred starches.

Further, the grinding in the second step adopts a cyclone type air flow grinder, a ball mill, a circulating pipe type grinder or a flat type air flow grinder; the grain size of the nano anhydrous starch is less than or equal to 100 nm. The grinding process can adopt a grinder or a ball mill, and the grain diameter of the nano anhydrous starch is ensured to be less than or equal to 100 nm. The anhydrous starch is ground to be nano-scale, so that the property uniformity of the water-resistant biological starch plastic is prevented from being influenced due to small particle size, and the nano-scale material is large in specific surface area and beneficial to later-stage degradation.

Further, the stearic acid, the paraffin, the polyethylene wax and the nano anhydrous starch in the third step are (6-7), (4-5) and (54-58) in sequence by mass. By introducing higher amount of stearic acid, paraffin and polyethylene wax into the starch, the nano anhydrous starch can be prepared into slurry, and the nano anhydrous starch is fully dispersed by a high-pressure homogenizer so as to be fully permeated by the stearic acid, the paraffin and the polyethylene wax. Not only the plasticity of the starch is increased, but also the hydrophobicity of the starch is improved. In order to prepare starch into slurry, a large amount of oil is used for penetrating and dispersing the starch, so that a lubricant does not need to be added in the subsequent extrusion processing. Fully dispersing the nano anhydrous starch by a high-pressure homogenizer, and enabling oily stearic acid, paraffin and polyethylene wax to permeate the starch.

Further, a plunger pump high-pressure homogenizer is adopted for high-pressure homogenization in the third step, the homogenization temperature of the plunger pump high-pressure homogenizer is 90-95 ℃, and the flow speed of slurry in the plunger pump high-pressure homogenizer is 100-200 m/s.

Further, the compatilizer in the fifth step is at least one of maleic anhydride grafted polyethylene, maleic anhydride grafted EVA and maleic anhydride grafted EAA; and the extruder in the fifth step is a co-rotating double-screw extruder with the length-diameter ratio (L/D) of 35-40. By adding the compatilizer, the water-resistant thermoplastic starch is dispersed in the polyethylene more uniformly.

Maleic anhydride grafted polyethylene: a plurality of maleic anhydride molecules are grafted on a polyethylene molecular chain by means of chemical reaction, so that the product has the good processability and other excellent performances of polyethylene, has the re-reactivity and strong polarity of a maleic anhydride polar molecule, is favorable for being used as a coupling agent and a re-reaction modifier, and has wide application in the field of plastics.

The maleic anhydride grafted EVA is the ethylene-vinyl acetate copolymer grafted maleic anhydride.

The maleic anhydride grafted EAA is the ethylene acrylic acid copolymer grafted maleic anhydride.

Further, the temperature of a first zone of the co-rotating twin-screw extruder is 130-140 ℃, the temperature of a second zone is 140-150 ℃, the temperature of a third zone is 160-165 ℃, the temperature of a fourth zone is 170-175 ℃, the temperature of a fifth zone is 140-150 ℃, and the temperature of a head is 120-130 ℃.

Further, the rotating speed of a main machine of the co-rotating double-screw extruder is 220-250 rpm, and the main feeding rotating speed is 20-30 r/min.

In a second aspect of the invention, a water-resistant biological starch plastic is provided, which is prepared by the preparation method.

The water-resistant biological starch plastic has the advantages of good water resistance, heat resistance and uniform performance. The crystal water in the starch is completely removed by drying, the starch is ground and refined to obtain the nano anhydrous starch, most of crystal structures of the starch disappear after the nano anhydrous starch is subjected to nanocrystallization, and the crystallinity of the starch is reduced and disappeared, so that the starch has thermoplasticity. Furthermore, the oil liquid formed by melting stearic acid, paraffin and polyethylene wax is used for fully dispersing and permeating the nano anhydrous starch under the action of a high-pressure homogenizer, so that the starch is endowed with good hot workability and hydrophobicity. The water-resistant biological starch plastic is not plasticized by using a polar micromolecule plasticizer, but completely removes crystal water from starch, nanocrystallizes the crystal structure, disperses the nano starch by using an excessive water-resistant lubricating material, and improves the water resistance of the obtained starch plastic.

As mentioned above, the water-resistant biological starch plastic and the preparation method thereof have the following beneficial effects:

1. the preparation method modifies the starch in advance to ensure that the modified starch is resistant to water and heat and has certain thermoplasticity, and then the modified starch is mixed with polyethylene for extrusion to prepare the water-resistant biological starch plastic which has the advantages of good water resistance, heat resistance and uniform performance.

2. Completely removing crystal water in the starch by drying, and grinding and refining the starch to obtain the nano anhydrous starch. Most of the crystalline structure of starch disappears due to nanocrystallization, at which point the starch has theoretical thermoplasticity, but it is still difficult to directly thermoplastically process. And then adding the nano anhydrous starch into an oily mixture (formed by mixing excessive stearic acid, paraffin and polyethylene wax), and dispersing by using a homogenizer to completely disperse the nano anhydrous starch in the composition of the stearic acid, the paraffin and the polyethylene wax to obtain the waterproof thermoplastic starch. Stearic acid is used as a plasticizer to modify the starch, so that the modified starch has good plasticity. The polyethylene wax has excellent cold resistance, heat resistance, chemical resistance and wear resistance, and can be used as a lubricant, and the polyethylene wax has stable chemical property and good electrical property. The polyethylene wax is used as a lubricant to ensure that the starch is uniformly dispersed in the oily mixture, so that the dispersibility of the starch is improved, and the agglomeration phenomenon is avoided. The paraffin has certain water resistance, and can also be used as a plasticizer and a dispersant.

3. And mixing the water-resistant thermoplastic starch, polyethylene and the compatilizer, and performing screw extrusion granulation to obtain the water-resistant biological starch plastic. The water resistance of the water-resistant biological starch plastic is improved by breaking the crystalline structure of the starch through nanocrystallization and uniformly dispersing the nano starch by using excessive water-resistant lubricating materials because the water-resistant thermoplastic starch is not plasticized by using a small-molecule plasticizer.

Drawings

FIG. 1 shows a polarization microscope photograph of the nano anhydrous starch of example 6, in which "cross spots" almost completely disappeared;

FIG. 2 is a view showing a polarizing microscope of anhydrous starch in comparative example 2, showing more "cross points";

FIG. 3 shows a schematic process flow diagram of the present invention.

Detailed Description

The present invention will be described in further detail with reference to specific embodiments, but it should not be construed that the scope of the present invention is limited to the following examples. Various substitutions and alterations can be made by those skilled in the art and by conventional means without departing from the spirit of the method of the invention described above.